This Core is the central element of our P01 application. It is responsible for generating, identifying, and preserving the mouse infertility models that will be used by the three Projects, and which will be made available. The cornerstone of the Core is to generate large numbers of mutant mice and conduct a genome-wide scan for mutations causing sterility in mice. The second major component is phenotyping of infertility mutants, and to classify them for possible subsequent analysis by one of the three Projects. Mutations will be validated genetically, and then either expanded for further detailed studies by one or more of the Projects, or cryopreserved and offered to the community at large through personal contacts and the Program Project Website.